Balanced Interconnects??

Single ended (RCA) cables carry the entire waveform, not just the + or - side of the signal. A balanced (XLR) cable carries the + half on one conductor and the - half on another. This allows for some small reduction in noise picked up by longer cables in that the + and - halves of the signal can be compared and any common noise between them can be summed (cancelled) at the input of the next component. This also applies to a "fully balanced" component. This is only true if the next component's input uses both halves of the signal. On some components where throwing in some XLR jacks is an afterthought, they simply use one leg of the signal. Components can also be balanced. If not, a splitter has to be used to output a balanced signal. My experience is that balanced sounds better on some components and single ended better on others. If you use long interconnects, some small reduction in noise is also possible.

Your balanced cable description is correct, Rockvirgo; however, your description of single-ended cables is wrong. Just before a balanced output the entire waveform is physically split into two voltages, opposite in polarity and equal in magnitude with respect to ground. A single-ended output simply sends the entire waveform through one conductor and a ground. You don't need to carry each half on a separate conductor unless you want to benefit from "common mode rejection", afforded by balanced transfer of the signal.